[amsat-bb] How you wind it

Robert Bruninga bruninga at usna.edu
Thu Oct 9 14:04:34 UTC 2014

How you wind a coil makes a BIG difference.

Ever wonder why your projects don’t work like the authors?

Im winding 42 turns onto a 1 Megohm 1/4W resistor to make a loading coil to
make a 5’ whip antenna on a cubesat tune to 28 MHz.

I was getting nowhere trying to add and subtract turns.  With a bandwidth
of only 200 kHz it was inconsistent getting to 28.120 center freq.

Then I simply took the same length of wire and tried 3 methods all with the
same number of turns.

1, down-and-back-and forward for 3 layers = 24.5 MHz

2, left-to-right but scrambled 3 layers along the way = 30.0 MHz

3, just a little squeezing of turns that had loosend = 28.8 MHz

Wow, just changing the winding method moves the 0.2 MHz bandwidth as far as

The difference of course is the stray capacitance between the end turns.

So winding method is important!

Just thought I’d share the results…


More information about the AMSAT-BB mailing list